I've recently (April 28, 2013) drawn a 2nd cartoon delta V map, this one with an emphasis on EML1 and EML2.-
On the right is 5261 Eureka, a Martian Trojan. This asteroid lies in
Mars' orbit trailing Mars by 60 degrees. Although it's the same
distance as Mars and the Martian moons Phobos and Deimos, note the
martian moons are closer in terms of delta vee. This is because of the Oberth effect.
Small bodies are more easily reachable in terms of delta vee because of
their shallow gravity wells. And, oddly enough, small bodies orbiting a
steep gravity well are even more accessible. In addition to the Oberth effect, planets can shed delta vee via aerobraking.-
In terms of delta vee, the Martian moons Phobos and Deimos are
closer than the Moon, Mars and most Near Earth Asteroids. Their low
density suggest they may be volatile rich. If so, their volatiles could
be exported to the Earth Moon L1 point and other locations in near
Earth space.-
What I call Low Mars orbit is a circular equatorial orbit 300 kilometers above the Martian surface.-Mars
Capture Orbit has a 300 kilometer altitude periapsis (the orbit's
closest point to Mars) and a 570,000 kilometer altitude apoapsis (the
orbit's farthest point from Mars). When an object in this orbit reaches
periapsis, it is going very nearly the surface escape velocity of Mars.
This maximizes the advantage of the Oberth effect. Mars capture orbits
can be easily reached from the Earth-Mars Hohmann transfer orbit. The
Hohmann is rarely accessible to a specific Mars capture orbit, though
(The orbit periapsis would have to be in the right position at the
right time). -
Earth Capture Orbit has a 300 kilometer altitude periapsis and a
900,000 kilometer altitude apoapsis. Like the Mars Capture Orbit, this
orbit maximizes the Oberth effect. Earth capture orbits are very easily
reachable from both the Mars and Venus Hohmann orbits. But also like
the Mars Capture Orbit, the Hohmann orbits are not easily reachable from a
specific capture orbit unless its periapsis is at the right time and place.-
The Earth-Mars Hohmann orbit is a minimum energy path from the Earth to
Mars. Launch windows for these orbits occur about every 2 1/8 years.
The trip takes about 7 months.-
The Earth-Moon L4 and L5 points are stable Lagrange points
on the Moons orbit, leading and trailing the moon by 60 degrees. The
Earth-Moon Lagrange points are locations where the Moon's gravity, the
Earth's gravity and centrifugal force all balance.-
The Earth-Moon L1 point is a Lagrange point between the Earth and the
Moon. It hovers above a fixed point on the Moon's surface. A lunar mass
driver aimed at the L1 will remain aimed at that point 365 days a year,
24 hours a day. Lunar oxygen, silicon and other materials could be
exported to that point. L1 moves slower than a natural orbit at that
altitude (.86 vs 1.1 km/sec), so it's easier to export cargo from the L1 to lower earth
orbits. In terms of delta vee, the Lagrange points are close to each
other as well as close to the Mars and Venus Hohmann transfer orbits.
Much of my interest in the L1 is due to an essay Rand Simberg wrote.-
The Earth-Venus Hohmann is the minimum energy path from Earth to Venus.
It requires a little less delta vee than the Mars Hohmann. The trip
takes about 5 months. The period of this orbit is very close to .8
years. The Earth-Venus synodic period is very close to 1.6 years, almost
exactly twice the period of the Hohmann orbit. This makes a system of
five Earth-to-Venus cyclers possible. The Earth encounter points are at
the tips of a beautiful, slowly rotating, five pointed star. See The Case For Venus for more details.-
The Venus Capture Orbits have a 300 kilometer periapsis and a 600,000
kilometer apoapsis. Like the Earth and Mars capture orbits, this orbit
maximizes the Oberth delta vee savings. Via aerobraking, these orbits
can be made into what I call Highly Eccentric Elliptical Venus Orbits.-
The Highly Eccentric Elliptical Venus Orbits have a 300 kilometer
periapsis and a 68,000 kilometer apoapsis. I believe five of these
orbits could be arranged to receive cargo and passengers from Earth to
Venus cyclers. Five more could be arranged for Venus to Earth cyclers.
These orbital period of a HEEVO is 2/5 the period of a High Venus
Orbit. In terms of delta vee, objects on HEEVOs could be some of the
most accessible in the solar system.-
High Venus Orbit is a circular orbit at 68,000 kilometer altitude.
This orbit is resonant with the HEEVO orbits and could pass by each
HEEVO at apoapsis. This orbit could be used to transfer
passengers from one HEEVO to another.-
Venus hasn't even been on my radar screen for years due to it's hostile
surface. Because of aerobraking and the
Oberth effect, near Venus asteroids can be captured to Venus' orbit
with relatively little delta vee. Once captured they're more accessible from Earth than most NEOs. Please see The Case For Venus. Geoffrey Landis has also pointed out
Venus has a hospitable temperature and pressure 50 kilometers
above it's surface (although the sulfuric acid clouds are a problem)
and suggested floating cities at that altitude. My delta vee map above
adds a 2 kilometer/second atmospheric drag/gravity penalty for
ascending through Venus' atmosphere. This is based on ascension from
a floating Landis city. Ascending from Venus' actual surface would
incur a higher penalty. -2003 SM84 is a near Earth Asteroid with a low inclination, eccentricity, and
a semi major axis close to 1 A.U. In other words it has an Earth-like
orbit. Such asteroids can be very close in terms of delta vee.
Unfortunately, low energy launch opportunities are rare if the
asteroid doesn't have an earth resonant period. For example an asteroid
with a 3/2 year period can pass near the Earth every three years, or an
asteroid with an 5/4 year period can fly by the earth every 5 years.
SM84's period isn't a simple fraction of earth's period. It will have a
good launch window in 2052. Please see my page The Case For Asteroids.-
What I call Low Earth Orbit is an equatorial circular orbit 300 kilometers above the earth's surface.-